The reliable containment of high-temperature pressurized gases is an important factor in the design and operation of piping and reactor systems in many diverse industries. Temperature cycles occur in these systems during startup, shutdown, and process upset conditions, and such cycles also may occur during normal process operations. The piping and process equipment in these systems often are constructed of various materials, many of which have different coefficients of thermal expansion. Couplings and joints between components with different coefficients of thermal expansion are problematic, especially when subjected to large temperature cycles. In order to minimize gas leakage, careful design of these couplings and joints is required.
Certain high-temperature systems such as ceramic gas separation membrane systems, ceramic membrane reactor systems, and solid oxide fuel cells utilize ceramic components operating at high temperatures. Gas flow to and from these ceramic components typically is provided by metal alloy piping systems, thereby requiring ceramic-to-metal joints. Because ceramic materials and metals usually have different thermal expansion characteristics, proper sealing at these ceramic-to-metal joints presents significant challenges in the design and operation of these systems. The seals at these joints must be reliable at high operating temperatures and must tolerate thermal cycling in order to achieve stable performance over the anticipated operating life of the system. In addition, the performance of these seals should be verifiable at room temperature during apparatus construction, and the seals should be economical and easy to assemble.
There is a need in the art of high-temperature gas processing for improved seals in couplings and joints between materials with different coefficients of thermal expansion. This need is addressed by the embodiments of the invention as described below and defined by the claims that follow.